1. Field of the Invention
The present invention relates to imide compounds, to a process for the production of the imide compounds from .beta.-aspartylphenylalanine derivatives (.beta.-AP derivatives), and to a process for the production of .alpha.-aspartylphenylalanine derivatives (.alpha.-AP derivatives) from the .beta.-AP derivatives.
2. Description of the Background
Many processes are known for producing .alpha.-L-aspartyl-L-phenylalanine methyl ester (.alpha.-APM) which is useful as a sweetening agent. Many of the conventional processes comprise protecting the amino group of L-aspartic acid (L-Asp) by some means, for example, with a carbobenzoxy group, a formyl group, a hydrogen halide, or the like, and then dehydrating and condensing the protected aspartic acid with L-phenylalanine methyl ester to obtain an N-protected-L-aspartyl-L-phenylalanine methyl ester. Removal of the protective group then yields .alpha.-APM. However, in all of these processes, the formation of .beta.-L- aspartyl-L-phenylalanine methyl ester (.beta.-APM) as a by-product is inevitable.
Another method which is known involves the conversion of a .beta.-aspartylphenylalanine derivative (formula (2)) into an .alpha.-aspartylphenylalanine derivative (formula (3)) and an .alpha.-aspartylphenylalanine anhydride derivative (DKP derivative) as shown in the following equation. This process is described in Japanese Patent Application Laid-open No. 277696/1986. ##STR2##
Although the .alpha.-AP derivative may be converted into
the desired .alpha.-APM easily and in high yield, when the DKP derivative is employed as a reactant, it gives only a low yield of .alpha.-APM and large amounts of by-products are formed in the reaction. Further, the by-products which form are changed into substances which can never be converted into .alpha.-APM. Therefore, in order to maximize conversion to .alpha.-APM, the conversion of material into the DKP derivative is to be avoided.